Quadratus lumborum m.

The Quadratus lumborum is a muscle in the lower back. It is irregular and quadrilateral in shape, and broader below than above. It originates from the lower border of the last rib for about half its length, and by four small tendons from the apices of the transverse processes of the upper four lumbar vertebrae. It inserts via aponeurotic fibers into the iliolumbar ligament and the internal lip of the iliac crest for about 5 cm.

Anterior to the Quadratus lumborum are the colon, the kidney, the Psoas major, psoas minor (if present), and the diaphragm; between the fascia and the muscle are the twelfth thoracic, ilioinguinal, and iliohypogastric nerves.